Deleting element from ArrayList

Question

I'm trying to copy 'select' elements from hands[1] to hands[0]. I can successfully do this with this code:

       for(Card card : hands[1].cards) {
          if (card.suit().ordinal() == 0){
             hands[0].addSingleCard(card);
             //hands[1].removeSingleCard(card);
             }
       }

Unfortunately, my removeSingleCard method doesn't work how i expected. With it commented out, the for-each loop successfully copies all 'Club' cards from hands[1] to hands[0]. I was hoping the removeSingleCard method would delete each 'Club' card from hands[1] after it was copied.

       public void addSingleCard(Card card){
           if(card!= null){
             cards.add(card);
           }
       }

       public void removeSingleCard(Card c){
           if(c!= null){
             cards.remove(c);
           }
       }

Any ideas why this isn't working?

The card.suit().ordinal() == 0 test is unidiomatic. Just use card.suit() == Suit.CLUBS. If you defined your suits in a different order, use the 0th element in the enum. Any use of Enum.ordinal() should arouse suspicion. — Eric Jablow
– Eric Jablow, Commented Apr 25, 2013 at 5:50

Jon Skeet · Accepted Answer · 2012-11-17 13:49:50Z

6

You can't remove from a collection you're iterating over, other than via the iterator. So you could use:

for (Iterator<Card> iterator = hands[1].cards.iterator();
     iterator.hasNext(); ) {
    Card card = iterator.next();
    if (card.suit().ordinal() == 0) {
        hands[0].addSingleCard(card); // Or hands[0].cards.add(card);
        iterator.remove();
    }
}

answered Nov 17, 2012 at 13:49

Jon Skeet

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1 Comment

binary101 Over a year ago

Ah nice :) This is awesome. Its exactly what i was trying to achieve. Thanks so much. I definitely need to remember this :D

Cratylus · Accepted Answer · 2012-11-17 13:50:07Z

2

I assume that you get a ConcurrentModificationException since you are removing from a collection while you are iterating in the for loop.
You should use iterator.remove

answered Nov 17, 2012 at 13:50

Cratylus

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